Figure 5.

Dual MHC-reactivity and coreceptor-dependence of MM14.4 TCR. (A) CD4⁺, MM14.4 T cells recognize Ab MHC class II molecules, while CD8⁺, MM14.4 T cells recognize K^k MHC class I molecules. T cell lymphoma cells transfected with MM14.4 TCR chains alone (double-negative, DN) or cotransfected with CD4 or CD8 c-DNA were tested for IL-2 production in response to MHC class II and class I molecules (left). Reactivity of CD4⁺ cells was inhibited by anti-A^b and anti-CD4 mAb (middle), while reactivity of the CD8⁺ cells was inhibited by anti-K^k and anti-CD8 mAb (right). Color conversion of Alamar Blue by IL-2–dependent cell line was used to measure IL-2 in culture medium. CD8 was a CD8α,β dimer transcribed from a polycistronic matrix. (B) Recognition of MHC class II by MM14.4 required CD4 interaction with MHC class II molecules. CD4⁺ MM14.4-transfected T cells reacted to A^b-positive stimulators (B6 or WT A^b-transgenic, A^{b WT}) but not to stimulators that expressed A^b with inactivated CD4 binding site (A^{b MUT}; left). The presence or absence of CD4 did not matter for activation with plate-bound anti-CD3 antibodies (right).